The present invention relates to a steering wheel with a metallic skeleton, which comprises a hub region, spokes and a rim and which is produced by casting in one piece with a U- or V-shaped cross-section open at least in the rim region.
In such steering wheels, the skeleton generally consists of light metal alloys based on aluminum or magnesium, which are designed in view of the requirements of die casting and also with regard to expected mechanical stresses. The steering wheels have a covering preferably of a foamed plastic that has only a minor, if any, contribution to mechanical strength. The mechanical forces are substantially taken up by the steering wheel skeleton, with not only the steering forces occurring on normal operation having to be taken into account, but also stresses that occur in the case of an impact of the vehicle driver in a vehicle crash.
On the other hand, one of course endeavors to make the steering wheel as light weight as possible and to achieve throughout as good a utilization of the material strength as possible, it still of course being taken into account that in modern steering wheels the spokes are not distributed uniformly over the circumference of the rim, so that a particularly careful structural design is necessary for the unsymmetrically supported steering wheel rim.
The production of the skeleton by casting techniques offers a large amount of design freedom, which hitherto in fact has not yet been utilized consistently enough.
From crash tests and from examination of steering wheels deformed or destroyed in accidents, it is known that portions of the steering wheel rim lying above and below in the normal position of the steering wheel are exposed to particularly high stresses with an impact.
The present invention provides an improved steering wheel wherein the strength of the skeleton has been optimized taking into account these findings, with a minimum expenditure of material.
According to the invention, the rim of the skeleton in the upper and lower portions, has a cross-section open towards the driver side of the steering wheel and in lateral portions has a cross-section open towards the opposed rear face of the steering wheel and away from the driver side of the steering wheel.
In this way, it is achieved that the material at the open end of the U- or V-shaped section is not loaded with tension but with compression, which in the case of metal parts produced by casting technique means a substantially better utilization of the material characteristics and in particular is advantageous in the portions of the steering wheel which experience the highest deformation under forces from the driver side.
As far as the lateral portions of the steering wheel are concerned, on the other hand, maximum stress occurs on the rear face of the steering wheel, so that here the maintaining of the profile open towards the rear, i.e. away from the driver side of the steering wheel, is preferred. Between the regions open towards the front and the rear, respectively, an H-shaped section is provided, the cross-piece of which constantly changes its level, so that viewed in circumferential direction, for example a U-shaped section transforms continuously into an H-shaped section and then into an inverse U-shaped section.
By the profiling according to the invention, with a cross-sectional area of the steering wheel rim being of equal size substantially over the entire circumference, an optimum adaptation can be carried out to the various stresses occurring, in particular in the case of a crash. As a result of the optimum utilization of material, generally in addition a reduction to the overall expenditure of material can be realized.